prefix.h (1942B)
1 /* Copyright 2013 Google Inc. All Rights Reserved. 2 3 Distributed under MIT license. 4 See file LICENSE for detail or copy at https://opensource.org/licenses/MIT 5 */ 6 7 /* Functions for encoding of integers into prefix codes the amount of extra 8 bits, and the actual values of the extra bits. */ 9 10 #ifndef BROTLI_ENC_PREFIX_H_ 11 #define BROTLI_ENC_PREFIX_H_ 12 13 #include "../common/constants.h" 14 #include "../common/platform.h" 15 #include "fast_log.h" 16 17 #if defined(__cplusplus) || defined(c_plusplus) 18 extern "C" { 19 #endif 20 21 /* Here distance_code is an intermediate code, i.e. one of the special codes or 22 the actual distance increased by BROTLI_NUM_DISTANCE_SHORT_CODES - 1. */ 23 static BROTLI_INLINE void PrefixEncodeCopyDistance(size_t distance_code, 24 size_t num_direct_codes, 25 size_t postfix_bits, 26 uint16_t* code, 27 uint32_t* extra_bits) { 28 if (distance_code < BROTLI_NUM_DISTANCE_SHORT_CODES + num_direct_codes) { 29 *code = (uint16_t)distance_code; 30 *extra_bits = 0; 31 return; 32 } else { 33 size_t dist = ((size_t)1 << (postfix_bits + 2u)) + 34 (distance_code - BROTLI_NUM_DISTANCE_SHORT_CODES - num_direct_codes); 35 size_t bucket = Log2FloorNonZero(dist) - 1; 36 size_t postfix_mask = (1u << postfix_bits) - 1; 37 size_t postfix = dist & postfix_mask; 38 size_t prefix = (dist >> bucket) & 1; 39 size_t offset = (2 + prefix) << bucket; 40 size_t nbits = bucket - postfix_bits; 41 *code = (uint16_t)((nbits << 10) | 42 (BROTLI_NUM_DISTANCE_SHORT_CODES + num_direct_codes + 43 ((2 * (nbits - 1) + prefix) << postfix_bits) + postfix)); 44 *extra_bits = (uint32_t)((dist - offset) >> postfix_bits); 45 } 46 } 47 48 #if defined(__cplusplus) || defined(c_plusplus) 49 } /* extern "C" */ 50 #endif 51 52 #endif /* BROTLI_ENC_PREFIX_H_ */